How the Index is Calculated 

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Water Quality and Quantity Monitoring

The water quality and quantity monitoring is done as part of the Organization for the Assabet River's long-standing water quality monitoring program. For most of its 15 years OAR's monitoring program has concentrated on the mainstem of the Assabet River - for good reasons - now, under the StreamWatch program, the focus has moved upstream to include the tributaries.

Water Quality: "Water quality" includes the chemical and physical properties of water in the streams. Once a month from May till September, OAR volunteers take water samples at the monitoring sites on the nine StreamWatch project streams and 12 sites along the mainstem Assabet River.

Water quality parameters tested include:

Streamflow:
Streamflow is the volume of water moving past a point in the stream at any given time. To measure streamflow, OAR's volunteers read staff gages once a week from June to September. A staff gage measures the height ("stage") of the water in a stream. Streamflow in cubic feet per second is calculated from the staff gage readings and a rating curve relating stage to flow. The rating curves for each monitoring site are being developed by USGS and OAR.

Groundwater levels:
Groundwater level data is downloaded from the USGS real-time web page for the groundwater monitoring well in Acton.

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